Mating and oviposition of a breeding strain of black soldier fly Hermetia illucens (Diptera: Stratiomyidae): polygynandry and multiple egg-laying

Black soldier fly (BSF), Hermetia illucens, is a promising species to valorise organic wastes and agricultural co-products into nutrient-rich animal feed. Thus, basic knowledge of its reproductive behaviour is needed to optimize its rearing processes and future selection. In this study, we investigated the reproductive behaviour (mating and egg-laying) of a mass-breeding BSF strain to (1) determine whether their females were monandrous or polyandrous, (2) describe the impact of multiple mating on egg production and fertility, and (3) describe where and when caged individuals mate and lay eggs. Newly emerged adults were individually tagged with acrylic paint to monitor their mating and egg-laying behaviour during their entire lifetime. Our results indicate that adults mated on average three times before dying, with different or even former partners. Some of them mated up to nine times. We also provide the first observation of multiple egg-laying for domesticated H. illucens females and show that virgin females can lay unfertilized eggs, in smaller quantities compared to mated ones. Finally, this study provides the first evidences that H. illucens can be polygynandrous and that multi-mated females can lay eggs several times, thus increasing egg production, in mass breeding conditions.